With the continuous development of times, the positioning technology is increasingly concerned. High-accuracy positioning demands, especially meter-scale positioning accuracy, raise higher technical requirements on wireless positioning.
For the GPS positioning technology, due to causes such as signal loss, under the situation that indoor signals become weak, a positioning terminal cannot find enough satellites; for a cellular network system, due to very great errors, higher accuracy cannot be achieved both outdoors and indoors, and the wireless positioning demands cannot be satisfied.
In order to solve the problem of indoor high-accuracy positioning, a wireless positioning system needs to be established on the ground. Each positioning signal station of the ground wireless positioning system is arranged near the ground. There are various ways for establishing a wireless positioning network, including adopting a satellite-system ground pseudo satellite system, a wireless local area network system, etc., herein the ground pseudo satellite system requires mobile phones to be capable of processing coexistence of signals from ground satellites and space satellite and raises a very great requirement on a dynamic range thereof. And the wireless local area network system mainly adopts a ranging method based on signal intensity, the positioning accuracy greatly depends on the density of arranged networks, and which has a very great requirement for the costs of positioning networks.
Communication networks have good coverage. However, the existing communication networks mainly are orientated to communication demands, there are few studies on positioning demands. Positioning errors of communication networks are within a range of a hundred of meters to thousands of meters, and indoor and outdoor positioning demands cannot be satisfied. As a result, communication networks are located at marginal positions in the field of positioning. If the positioning accuracy is improved by increasing the density of communication networks, the great network construction costs will be required and simultaneously the interference between networks will be increased.
Table 1 shows a positioning mode supported in the current LTE standard (source: 3GPP TS 36.305 V12.0.0 (2013-12).
In Table 1, A-GNSS: based on a navigation satellite positioning mode, a satellite signal receiving positioning terminal measures arrival time of a satellite signal, then calculates a location of the positioning terminal according to navigation teletext information and then transmits a result to a positioning center through radio communication. A downlink positioning mode (Downlink): a positioning terminal measures a downlink signal of an LTE base station and sends a measurement result to a positioning center, and in current standards, a UE-assisted mode, i.e., a mode of performing positioning through a positioning center (E-SMLC) assisted by UE, is only supported for the Downlink positioning mode. An enhanced cell ID positioning mode (ECID): positioning is performed according to cell ID and the positioning accuracy is lower. An uplink positioning mode (Uplink): a base station measures signals of a positioning terminal and then sends the signals to a positioning center.
TABLE 1Realization featureUE-assisted,LMU-RealizationUE-E-SMLC-eNB-assisted/E-modebasedbasedassistedSMLC-basedSUPLA-GNSSYesYesNoNoYesNote 1(UE-based andUE-assisted)DownlinkNoYesNoNoYes (UE-assisted)E-CIDNoYesYesNoYes (UE-assisted)UplinkNoNoNoYesNo
From Table 1, it can be seen that, except A-GNSS, LTE does not support the UE-based positioning mode, i.e., in a Downlink or Uplink mode, positioning must be realized in the positioning center (E-SMLC), through networks. Under scenarios of poor communication conditions, such as great fading and interference, the above-mentioned positioning mode cannot realize positioning of a positioning terminal. As a result, the positioning mode of LTE restricts the realization of positioning by using an LTE system.